Andreas W. Momber

Principles of abrasive water jet machining

Preface.- Nomenclature.- Introduction.- Classification and Characterization of Abrasive Materials.- Generation of Abrasive Water Jets.- Structure and Hydrodynamics of Abrasive Water Jets.- Material-Removal Mechanisms in Abrasive Water-Jet Machining.- Modeling of Abrasive Water Jet Cutting Processes.- Process Parameter Optimization.- Geometry, Topography and Integrity of Abrasive Water-Jet Machined Parts.- Alternative Machining Operations With Abrasive Water Jet.- Control and Supervision of Abrasive Water-Jet Machining Processes.- References.

On-line analysis of hydro-abrasive erosion of pre-cracked materials by acoustic emission

Acoustic Emission (AE) sensing technique is used as a tool for on-line monitoring of hydro-abrasive erosion (HAE) of pre-cracked multiphase materials. As reference materials, five types of concrete materials were used for the experimental study. Compression tests were performed to determine the mechanical properties and the failure behavior of these materials. Erosion parameters, such as abrasive particle velocity, local exposure time, and abrasive mass flow rate were varied during the experiments and AE-signals were acquired. The trends exhibited by the time domain and frequency domain AE-signals with change in process parameters and material properties were analyzed. The results indicate that acoustic emission signal is capable of revealing the diAerent material removal mechanisms occurring in pre-cracked multiphase materials when subjected to hydro-abrasive erosion. Visualization studies performed on the erosion site provide more insight into the physics of the process and verify the observations made from the AE-signals. Finally, it is concluded that due to its capability to quantify the amount of material removed, AERMS could be considered as a parameter for monitoring the material removal process. ” 1999 Elsevier Science Ltd. All rights reserved.

Statistical character of the failure of multiphase materials due to high pressure water jet impingement

In this study, fracture experiments on multiphase material samples have been carried out using high speed water jets. Based on fracture geometry measurements and on grain analyses it was found that the fracture of this type of materials by water jet impingement is a highly localized process at low pressure ranges. Beyond a critical pressure range of about 30 times the materials tensile strength a change in the material behaviour was observed. This result is in agreement with a theory suggested by Powell and Simpson. To explain the local character of the failure process, a simplified fracture model is introduced which resulted in a relation between a fracture probability parameter and the fracture width in the damaged materials.

An energy balance of high-speed abrasive water jet erosion

Abstract High-speed abrasive water jetting is an alternative tool for machining engineering materials. The energy dissipation processes involved in this erosion process have not been investigated systematically. In this paper, a model is developed to calculate the energy dissipation in workpieces eroded by abrasive water jets. By introducing an energy dissipation function χ(Φ). the model enables the estimation of the energy absorption as a function of the erosion depth. The energy dissipation function can be expressed by a second-order polynomial approximation. Measurements of the reaction forces on the exiting slurry after the erosion process, material removal experiments and fracture tests are conducted to separate the components of the energy dissipation parameter, such as damping, friction and erosion debris generation.

The kinetic energy of wear particles generated by abrasive–water-jet erosion

Abstract The kinetic energy of wear particles removed by the erosive action of a high-speed mixture of abrasive particles and water is estimated, based on a simple analysis and on impact-force measurements of the abrasive–water-jet before and during the material-removal process. The energy involved in the acceleration of the wear particles is about 0.3% of the input energy of the high-speed abrasive–water-jet. The kinetic energy of the wear particles that are removed increases linearly with the erosion depth.

Accelerated High Speed Water Erosion Test for Concrete Wear Debris Analysis

This paper contains investigations of wear particles generated during the erosive wear of four different concrete, mixtures by high velocity water flow at velocities of about 700 m/s.i The wear particles were collected, dried and analyzed by sieve experiments. Based on the sieve analysis, specific surface and average grain diameter of the particle samples were estimated. Using simple, comminution relations, the specific crack length of every sample is calculated. It is shown that all estimated parameters exhibit a strong relationship to characteristic material properties, such as compressive strength, Youngs modulus, and absorbed fracture energy. It was found by regression analysis that the average debris wear size can be effectively characterized by the absorbed fracture energy of the concrete sample. It is concluded that these relations are the result of different paths of fracture propagation through the materials during the generation of a microcrack network. Presented as a Society of Tribologists ...

Investigations in Abrasive Water Jet Erosion Based on Wear Particle Analysis

In the study, gray cast iron specimens are cut by abrasive water jets with pressures between p = 140 MPa and p = 345 MPa. Wear particles collected during cutting are analyzed based on average grain size and grain size distribution. The average diameter of the removed wear particles was found to be between D = 60 μm and D = 70 μm and drops with rising pump pressure. A semi-empirical model is developed to describe this relation. The grain distribution of the wear particles can be characterized by a Rosin-Rammler-Sperling (RRSB)-distribution. The surface area of the removed wear particle samples increases with an increase in the pump pressure. The progress drops at higher pressure levels indicating accelerated efficiency losses if the pump pressure exceeds a certain value. An efficiency parameter, Φ, is defined which relates the jet kinetic energy to the creation of the wear particles, and a method for its estimation is developed. It was found that the efficiency parameter exhibits a maximum value at a pressure level of about three times the material threshold pressure. The average efficiency parameter is estimated to φ = 0.02.

Quantification of Energy Absorption Capability in Abrasive Water Jet Machining

The paper contains a mathematical model for the estimation of the energy absorption capability of materials during abrasive water jet machining based on an energy balance inside the workpiece. A parameter χ(h) is defined to describe and calculate the energy absorption capability. A method for the estimation of this parameter is developed based on a parabolic striation model. It is shown that the energy absorption depends on the depth of cut following a second-order equation. The relation between the relative depth of cut h/hmax and the energy absorption capability χ(h) can also be described by a second-order equation. For such materials as aluminium, cast iron and stainless steel a critical point of abrasive water jet energy absorption is detected at a depth of cut of h = 0.52hmax, which corresponds to a striation angle of about 75°.

Particle-size distribution influence in high-speed erosion of aluminium

ABSTRACT The paper discusses the influence of the abrasive particle-size distribution on typical high speed abrasive-waterjet erosion parameters. The size distributions of the used abrasive particles are modelled by a Rosin-Rammler-Sperling (RRSB) grain-size distribution containing the distribution parameters D and n. Both parameters are independently varied to characterise different particle-size distributions. Aluminium specimens are eroded by abrasive-waterjets at velocities of 320 m/s, and the erosion depth, depth distribution, and the surface roughness are measured. The depth distribution and the surface roughness are very sensitive to the particle-size distribution parameters, whereas the average erosion depth is not influenced significantly. These results offer the possibility to select an “optimum” grain-size distribution for maximum surface quality at fixed kinematics conditions.

An acoustic emission study of cutting bauxite refractory ceramics by abrasive water jets

This article discusses the material removal process in bauxite refractory ceramics cut by abrasive water jets. Several parameters of the process were changed during the experiments. The experiments were monitored online by the acoustic emission (AE) technique. It was found that AE signals are able to sense the material removal process as well as the machining performances very reliably. Unsteady material removal mode consisting of matrix removal and intergranular fracture was very well represented in the AE signals by an unsteady time dependent signal type characterized by burst emissions and a frequency domain signal associated with a twin-peak shape. The particular characteristics of the signal depend on the energy involved in the process.